1. Field of the Invention
The present invention relates generally to hot platen presses and in particular to vacuum hot platen presses suited for manufacturing laminated boards or multi-layered electronic circuit boards.
2. Description of Related Art
There have previously been invented column type and window frame type vacuum hot platen presses. The vacuum hot platen press of a column type fundamentally provides four columns each of whose ends are connected to an upper stationary platen and a flange of a pressing cylinder respectively. A movable platen which moves up and down along the column and a plurality of heating platens are provided between the upper stationary platen and the movable platen.
A window frame of the vacuum hot platen press comprises a plurality of rectangular plates of tensile strength members providing a rectangular opening in which a platen moves against a stationary platen and a plurality of hydraulic cylinders.
Both vacuum hot platen presses of both the column type and window frame type provide process chambers which are enveloped by seal covers to be evacuated by a vacuum source. The upper and lower portions of the seal covers of a large vacuum hot platen press of the column type have hitherto been fixed with respect to an upper stationary platen and a flange of the pressing cylinders, which are held apart by four columns that determine the distance between them. The columns are not able to elongate freely, and during the pressing operation the bolts holding the seal covers may break and/or the columns may distort and this is especially a problem when the platen height exceeds 10 meters. Moreover, the seal covers are depressed by vacuum force likewise causing the bolts to be broken or the columns to be distorted.
Similarly, these effects take place in the large vacuum hot platen presses of the window frame type.
Consequently, such problems cause undesirable effects on the quality of laminated boards or multi-layered electronic circuit boards.